Supported cobalt sulfate desulfurization catalyst

ABSTRACT

A catalyst is provided which is useful in the direct single-step conversion of sulfur oxides to element sulfur. The catalyst comprises cobalt sulfate as an essential catalytic ingredient supported on an attrition resistant and decrepitation-resistant catalyst support wherein cobalt is present in an amount less than ten parts cobalt per hundred part by weight of catalyst.

BACKGROUND OF THE INVENTION

This invention relates to a desulfurization catalyst comprising cobaltsulfate as an essential catalytic ingredient supported on a catalystsupport. The catalyst permits the single-step conversion of sulfuroxides present as gases in stack gases and the like. By the term "sulfuroxides" we refer herein to both sulfur dioxide and sulfur trioxide. Thisone-step conversion of sulfur oxides, and particularly sulfur dioxide,to elemental sulfur which is not adsorbed on the catalyst but isdischarged as elemental sulfur in the effluent from the catalyst bed,eliminates the conventional second-step regeneration of a `catalyst` bedand reduction of sulfur loaded upon conventional metal oxide acceptors,or in the alternative, of conversion of catalytically produced H₂ S toelemental sulfur.

Conventionally, sulfur oxides are removed from gaseous mixtures such asstack or flue gases and smelter off-gases by contact with metal or metaloxide acceptors such as copper or copper oxide, respectively, on arefractory carrier material such as alumina. During contact, sulfuroxides are accepted by the metal or metal oxide, so that the purifiedgases, if discharged via a stack, cause substantially no air pollution.The metal sulfate, for example copper sulfate formed during acceptance,may be subsequently decomposd by means of reducing gas, the result beinga regenerated acceptor and a sulfur dioxide-rich gas, which can be used,for example, to produce elemental sulfur or sulfuric acid. Theregenerated acceptor can then be reused to purify a further quantity ofgas containing sulfur oxides. In this two-step prior art process, theregeneration of the acceptor oxide, which is sometimes referred to as`catalyst`, is a difficult problem which often forms combustibledeposits on the acceptor during the regeneration process. Thecombustible deposits are undesirable since their combustion during useof the regenerated acceptor causes a significant increase in temperaturewhich adversely affects the acceptor life. More importantly, thetwo-step process requires that an inordinate expenditure of time bedevoted to regeneration of the acceptor, the expenditure of which timeis an economic deterrent.

Even in those instances where a single-step conversion of sulfur dioxideto elemental sulfur may be effected with an appropriate catalyticcomponent suitably supported on a carrier, it has been found that theexotherms to which the catalyst is normally subjected, along with thereactions of the stack-gas components with the catalyst components,results in the decrepitation or disintegration of the catalyst so that abed of catalyst soon develops so high a pressure drop as to becomeunusable. The problem of selecting a catalyst which is stable, has adesirable activity which may be supported on a support which will notinterfere with the activity of the catalyst and yet defy attrition anddecrepitation, at the same time permitting a conversion of sulfurdioxide to element sulfur in excess of 90 percent, has been a problem towhich a great deal of effort has been devoted (see Removal of Sulfurdioxide from stack gases by Catalytic Reduction to Elemental Sulfur withCarbon Monoxide, Robert Querido and W. Leigh Short, "Ind. Eng. Chem.Process Des. Develop.", Vol. 12, No. 1, 1973). The catalyst of ourinvention is a solution to that problem.

U.S. Pat. No. 3,495,941 discloses a typical prior art desulfurizationcatalyst utilizing vanadium oxide supported on a carrier material. Alsodisclosed therein is cobalt molybdate which is disclosed for thereduction of sulfur dioxide with methane. In either case, sulfur dioxideis reduced to hydrogen sulfide which is thereafter converted toelemental sulfur.

Many chemical processes currently in commercial use employ catalystswhich undergo a change in crystalline structure during the course ofreaction. Such catalysts are particularly susceptible to attrition andother types of physical degradation. The desulfurization catalyst of ourinvention consists essentially of cobalt sulfate in crystalline formsupported on an attrition resistant support such as gamma-alumina.However, formed gamma-alumina shapes do not maintain their physicalstrength, particularly at elevated temperature operation up to about700°C, and thus are not sufficiently decrepitation resistant. By`attrition resistant` catalyst is meant that the catalyst resistsabrasion more or less, at or near the surface, while a general loss ofstrength of a shaped catalyst pellet is usually referred to asdecrepitation or disintegration. Decrepitation of a catalyst pelletoften permits it to be crushed by pressure between the thumb andforefinger. Numerous prior art catalysts have utilized clays of varioustypes as an ingredient for a catalytic support. In most instances, theclay containing support is used as a binder and the catalyst support isthereafter fired to decompose the catalytic ingredient present in theform of a salt or hydroxide to the oxide form. In particular, U.S. Pat.No. 3,146,210 to Baldwin teaches the preparation of attrition-resistantalumina, beryllia, and zirconia catalyst pellets which can be used ascatalyst supports by subsequent impregnation of the pellets withmetallic salts. Attrition resistance and the maintenance of the physicalstrength of a supported catalyst are serious problems to which muchattention has been devoted. Baldwin made no reference to the use of clayto enhance attrition and decrepitation resistance and thus, overlookedthe discovery that clays can provide surprising transverse and crushstrength to a tableted or pelleted alumina support.

The term "clay" when used in context with the present invention, is tobe interpreted in the broadest sense and this invention is not limitedby subtle differences and the composition of substances which were orcould be classified in the broad sense as clays. Thus, a clay may bedefined as "an earthy or stoney mineral aggregate consisting essentiallyof hydrous silicates and alumina, plastic when sufficiently pulverizedand wetted, rigid when dry, and vitreous when fired at sufficiently hightemperatures." Alternatively, a clay may be broadly defined as a"mixture of hydrous silicates of aluminum, iron, and magnesium with orwithout other rock and mineral particles, said clays being characterizedby extreme fineness of particles (often colloidal in size) and by widevariations in physical and thermal (ceramic) properties and in mineraland chemical composition." Other definitions of the term "clay" may befound in the following volumes and the references contained therein andsuch clays are useful in the present invention:

Thorpes Dictionary of Applied Chemistry, J. F. Thorpe and M. A.Whiteley, Volume 3, Fourth Edition, Longmans, Green and Co., New York(1953)

Encyclopedia of Chemical Technology, Kirk-Othmer, Volume 6, SecondEdition, Inter-Science publishers, New York (1965).

The preferred clays for use with our invention include: the kaolingroup, including for example, kaolinite, dickite, nacrite, anauxite,halloysite, and endellite; the montmorillonite group, including forexample, montmorillonite, beidellite, nontronite, hectorite, saponite,saucounite, and bentonite; the attapulgite and sepiolite group,including for example, attapulgite taken from the region of Attapulgus,Ga.; the high alumina clays, including for example, diaspore, boehmite,Gibbsite, and cliachite; and also the ball clays found principally inKentucky and Tennessee and the fire clays produced in Missouri,Illinois, Ohio, Kentucky, Mississippi, Alabama, and Arkansas. Mixturesof the forementioned clays are likewise useful in the present inventionas the clay portion of the binder.

SUMMARY OF THE INVENTION

It has been discovered that crystalline cobalt sulfate particlesdeposited on an attrition-resistant catalyst support permits the direct,single-step conversion of gaseous sulfur oxides to elemental sulfur inthe presence of reducing gas and requires no secondary recovery steps,and no regeneration of the catalyst.

It is therefore a general object of this invention to provide asupported catalyst, having cobalt sulfate as its essential catalyticingredient, for the desulfurization of stack-gases which typicallycontain nitrogen, sulfur dioxide, sulfur trioxide, carbon monoxide,carbon dioxide, oxygen and small quantities of other gases.

It is a specific object of the instant invention to provide a supportedcobalt sulfate desulfurization catalyst which is not affected by thepresence of reducing gases, relatively free of particulate matter,concurrently introduced into a gaseous stream containing sulfur oxides,and which is remarkably resistant to poisoning.

It is still another object of the instant invention to provide asupported cobalt sulfate catalyst which is effective with conventionalreducing agents including low molecular weight hydrocarbons, CO and H₂intermixed with stack gases or smelter off-gas; and, to provide acatalyst which is surprisingly insensitive to the concentration of SO₂,SO₃, H₂ S, minor quantities of COS and the like.

It is a specific object of this invention to provide a continuouslyoperable desulfurization catalyst which does not require burninghydrocarbons over the catalyst to regenerate it, thus avoidingdeposition of carbon on the surface of the catalyst.

It is a still more specific object to provide an impregnateddesulfurization catalyst containing as its essential catalyticingredient cobalt sulfate supported on a porous catalyst support byimpregnation thereof, so that the supported porous catalyst containsfrom about 1/2 to about 10 parts by weight cobalt per hundred parts byweight supported catalyst.

It has been discovered that calcined, porous gamma aluminaconventionally impregnated with coblat sulfate provides an immediatelyactive and effective desulfurization catalyst for the removal of inexcess of 90% of sulfur oxides from stack-gases, but suffers thedisadvantage of disintegrating relatively easily, so that its use,particularly in a packed bed reactor, is seriously limited.

It has also been discovered that an attritionresistant desulfurizationcatalyst support having relatively high surface area, high porosity andhigh crush strength, can be prepared by blending clay or a clay-talcmixture with gamma-alumina, adding sufficient moisture to make the blendpliant, shaping the pliant mixture into tablets or the like, andcalcining the tablets at a temperature above about 1000°C for a timesufficient to harden the support and give it physical strength.

It is therefore a general object of this invention to provide adesulfurization catalyst comprising cobalt sulfate as an essentialcatalytic ingredient supported on a mixture of calcined gamma-aluminaand clay, which mixture provides a porous catalyst support surprisinglyresistant to attrition and degradation, and, unexpectedly providesgreater stability and longer life than cobalt sulfate supported oneither gamma-alumina alone, or, on clay alone.

It is a specific object of this invention to provide a highly porous,attrition-resistant catalyst support impregnated with cobalt sulfatewhich is crystallized thereupon and which is present during use at alltimes, along with minor amounts of cobalt sulfide formed during use,which support retains its porosity during operation and does not get`loaded` as do metal oxide acceptors.

It is still another specific object of this invention to provide asupported cobalt sulfate desulfurization catalyst, the supportconsisting essentially of gamma-alumina and bentonite, and the supportedcatalyst having essentially the same crush strength before and after usein a desulfurization reactor.

These and other objects, features and advantages of this apparatus willbecome apparent to those skilled in the art from the followingdescription of preferred forms thereof and the examples set forthherein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

The supported cobalt sulfate catalyst disclosed herein is composedwholly of cobalt sulfate supported on an attrition-resistant catalystsupport. Calcined catalyst support is impregnated with cobalt sulfateand the impregnated catalyst is not thereafter calcined. The unsupportedcatalyst of the instant invention is not an effective catalyst. Itappears essential that the cobalt sulfate be supported sufficiently toprovide sufficiently dispersed active centers such as those providedwhen at least 50 percent by weight of the supported catalyst constitutescatalyst support. It is preferred that in excess of 90 percent by weightof the supported catalyst consist of support. Any known catalyst supportsuch as alumina, pumice, silicon carbide, zirconia, titania, alumina,bentonite, the inorganic phosphates, borates, and carbonates stableunder the reaction conditions, may be used but gamma-alumina ispreferred. Porous catalysts are preferred, catalysts with large porevolumes per unit weight of catalyst, though not necessarily of largepore diameter, giving the best results. Commercial gamma-alumina gradeshaving an average pore diameter of about 100A, with a pore volume inexcess of 0.6 ml/g and a specific surface area of from about 50-200m² /gare particularly suitable. Most preferred because of itsattrition-resistance, is a mixture of gamma-alumina and bentonite.Silica and supports containing a relatively large amount of silica suchas silica-alumina are substantially inferior catalyst supports for thepresent purpose, as is alpha-alumina.

In the preparation of the desulfurization catalyst useful in thisinvention, the cobalt sulfate can be blended together with the catalystsupport or can be formed in situ. Cobalt sulfate is the essentialcatalytic ingredient of the instant desulfurization catalyst and thecritical requirement is that the cobalt sulfate remains in a finelydivided crystalline form in the finished catalyst, without beingconverted to the oxide, though a minor amount of cobalt sulfide may beformed. It is distinct from cobalt oxide supported on a suitablesupport, which after continued exposure to sulfur oxides acts as anacceptor of sulfur and is progressively converted to cobalt sulfatewhich loads the catalyst support and must thereafter be driven off so asto regenerate the acceptor. In the catalyst of our invention, there isno step requiring activation of the catalyst because the catalyst isactive when impregnated, or regeneration of the loaded catalyst, becausethe catalyst is not loaded and the pores remain open.

The catalyst support may be prepared by any conventional method; it maybe extruded, tableted or spherodized, preferably in such a manner as toprovide good crush strength after the support is calcined. Attritionresistance of our catalyst is of especial importance where impregnatedcatalyst is used in a fluid bed reactor.

Whether the catalyst is to be used in a fluid bed or fixed bed reactor,active catalyst is formed simply by impregnating the calcined catalystsupport with cobalt sulfate, preferably in the form of a dilutedsolution so as to provide from about 1 to about 10 percent by weightcobalt on the catalyst support. Additional quantities of cobalt may beused but the economics of providing in excess of 10% cobalt do notjustify such an excess.

Impregnated catalyst is generally dried for convenience, prior to use ina reactor, and the extent to which it is dried is a matter of choice.Irrespective of the conditions of drying of the catalyst, thetemperature is insufficient to convert a significant amount of cobaltsulfate to cobalt oxide, and the catalytic activity is not enhanced bydrying at elevated temperatures.

Minor amounts of metal sulfates other than cobalt sulfate may be presentin the desulfurization catalyst but the presence of these minor amountsdoes not appear to enhance the activity of the catalyst, and nodeliberate effort is made to provide such additional materials. Duringoperation, a minor amount of cobalt sulfide is formed, generally lessthan 20 percent of all the cobalt present initially as cobalt sulfate.

The surprising advantage of the catalyst of this invention is that itpermits a one-step process for converting sulfur oxides to elementalsulfur at conversions in excess of 90 percent at very high massvelocities. This is particularly surprising because the sulfate anion isknown to sterically hinder catalytic activity of the cation. Theactivity of the catalyst is particularly insensitive to theconcentration of sulfur oxides to be converted. Essentially completeconversion of sulfur oxides, independent of their concentration, is ofparticular value in desulfurization of stack gases containing about 1%SO₂, and smelter off-gases which may contain about 15% SO₂ or more. Toeffect this one-step conversion, the stack-gases or smelter off-gasescontaining sulfur oxides are premixed with a sufficient amount ofreducing gas to reduce the sulfur oxides and to eliminate any oxygen oroxidizing gases present in the stack gases to be contacted with thecatalyst. Reducing gases such as are produced by partial combustion inprior art twostep processes, for example, the lower hydrocarbons havingfrom about 1 to about 5 carbon atoms, and more particularly methane,ethane, propane and butane, are preferred. H₂ S, H₂ and CO may also beused in place of the lower hydrocarbons, or in additions thereto, as isknown in the art, mixtures of CO and H₂ being preferred. The amount ofreducing gas used depends on the composition of the gas and the yield ofelemental sulfur desired. Sufficient CO and H₂ is provided to react withall oxygen present as SO₂, SO₃ or nitrogen oxides (NO_(x)). If O₂ ispresent, sufficient additional CO is added to convert it to CO₂, butexcess CO is to be avoided because it forms carbon oxysulfide (COS). Itis preferred to have a slight excess molar ratio of reducing gas tosulfur dioxide and other gases to be reduced, with only a very slightexcess of CO in the reducing gas. In general, less than 10% excess CO ispreferred.

It is essential, for the single-step conversion of sulfur oxidescatalytically to elemental sulfur, that CO be present in the reducinggas as a necessary reductant. Though CO is conveniently obtained byincomplete combustion of lower hydrocarbons it is preferred to tailorthe composition of stack gases so as to contain a substantial amount ofCO. Additional CO, as required, may be provided by the incompletecombustion of coal where lower hydrocarbons are uneconomic, or byregulated reduction in a bed of scrap steel, in a prior processing step.Yet another procedure which can be used with metallurgical smelters, isto use a bed of coke to generate the needed CO from unreacted oxygen.The choice of any of the foregoing methods of providing CO as areductant, all of which are known in the art, depends on the particularprocess, conditions and requirements of the desulfurizaton catalyst.

The temperature at which desulfurization is conducted may varyconsiderably depending upon the composition of the stack-gases, theparticular make up of the supported catalyst, the physicalcharacteristics of the reactor in which the catalyst operates, theparticular sulfur oxides present in the stack-gases, the particularreducing gases used and the correlated conditions of the rate ofthrough-put or contact time, and, the ratio of sulfur oxides to reducinggas. In general, when operating at pressure near atmospheric, that isfrom about -10 psig to about 100 psig, temperatures in the range fromabout 300°C to about 700°C may be advantageously employed. However, theprocess may be conducted at other pressures, and in the case wheresuperatmospheric pressures, e.g., above 100 psig, are employed, somewhatlower temperatures may be desirable. In the preferred embodiment wherethe process is employed to convert sulfur oxides to elemental sulfur,wherein sulfur dioxide is present in the range from about 10 to about 12percent, a temperature range of 400°C to 700°C has been found to bedesirable at about atmospheric pressure.

Typical stack gas and smelter off-gas compositions are as follows:

    Stack gas*   Copper Roaster                                                                              Copper Converter                                                Gas**         Gas**                                              Volume %     Volume %      Volume %                                           ______________________________________                                        SO.sub.2                                                                            0.25       SO.sub.2                                                                              7.25    SO.sub.2                                                                             5.5                                   SO.sub.3                                                                       O.sub.2                                                                            1.0                                                                     CO.sub.2                                                                            13.0                                                                    H.sub.2 O                                                                           10.0                                                                     N.sub.2                                                                            76.0                                                                    ______________________________________                                          * Flue Gas Desulfurization Technology", Hydrocarbon Processing, October,     1971                                                                          ** "Control of Sulfur Oxide Emissions from Primary Copper, Lead and Zinc      Smelters", Journal of the Air Pollution Control Association, Vol. 21, No.     4, April, 1971.                                                          

While pressure other than atmospheric may be employed, it is generallypreferred to operate at or near atmospheric pressure, since the reactionproceeds well at such pressures and the use of expensive high pressureequipment is avoided.

The apparent contact time employed in the process is not critical and itmay be selected from a broad operable range generally lower than contacttimes for gaseous desulfurization processes of the prior art. Theapparent contact time may be defined as the length of time in secondswhich the unit volume of gas measured under the conditions of reactionis in contact with the apparent unit volume of the catalyst. It may becalculated, for example, from the apparent volume of the catalyst bed,the average temperature and pressure of the reactor, and the flow ratesof the several components of the reaction mixture. The optimum contacttime will, of course, vary depending upon the composition of the stackgases to be treated, the physical and chemical condition of thesupported catalyst in the reactor, and the process conditions into whichdesulfurization is carried. An apparent contact time less than onesecond, and generally less than 0.1 second, suffices.

Water is formed as a product of reaction and it has been found not toaffect the course of the reaction adversely. The deliberate introductionof water in the form of steam, however, is to be avoided as the presenceof water in excess of the amount normally formed in the course of thereaction, appears to provide no advantage and often gives undesirableresults.

Though the desulfurization catalyst of the instant invention is operablewith any conventional attritionresistant catalyst support, it is foundthat silica and catalyst supports containing relatively large amounts ofsilica appear to affect adversely the performance of the catalyst.Though gamma-alumina is a desirable catalyst support and providesexcellent conversions and stability its lack of physical strength underoperating conditions results in attrition of the catalyst so that wherea fixed bed catalytic reactor is used, the pressure drop through thereactor builds up to over a period of time, to a level at whichoperation is impractical.

Suitable carrier materials are solids which are resistant to hightemperatures and which are not attacked by the compounds of the gaseousmixtures to be contacted with the catalyst. Examples of suitable carriermaterials are natural clays (whether or not acid pretreated), bauxiteand magnesia or synthetic alumina. Alumina, in particular gamma-alumina,is a suitable carrier except that it is not sufficiently attritionresistant for prolonged use, without being mixed with clay.

The surface area of our desulfurization catalyst is not critical, butlow specific surface area below about 50 M² / gram is not recommend forefficiency. Best results are obtained with a catalyst support having arelatively large specific area preferably, in excess of 100 M² /gram.

A particularly surprising aspect of this invention is the effect ofbentonite on the strength, durability and effectiveness of gamma aluminawith which it is combined to form the catalyst support. This effect ofbentonite is the more interesting because cobalt sulfate supported onbentonite alone, provides less than 90 percent conversion of sulfuroxides for the same amount of cobalt sulfate.

In general, any apparatus of the type suitable for carrying out thedesulfurization reaction in the vapor phase may be employed in theexecution of this process. The process may be conducted in either afixed bed or in a fluid bed reactor. A fixed bed reactor is preferredwherein the catalyst bed employs a large particulate or pelletedcatalyst. A fluidized bed of catalyst may be employed but control of thereaction is more difficult. The desulfurization process, whether used ina fixed or a fluid bed, may be conducted either continuously orintermittently. In a fixed bed reactor, the reaction is most preferablyconducted continuously until conversion of the sulfur oxides drops belowa predetermined level at which point the catalyst may be replaced, orfortified with an additional amount of fresh catalyst. Deactivatedcatalyst is not regenerated.

The catalyst composition of this invention is further illustrated in thefollowing examples wherein the amount of the various ingredients areexpressed as parts by weight unless otherwise specified.

EXAMPLE

Using a ribbon blender prepare a mixture containing 48 partsgamma-alumina, 10 parts bentonite and 3 parts milled Sterotex lubricant,by blending for about fifteen minutes. The loose and packed apparentbulk density (A.B.D.) of the mixture is in the range from about 0.3 toabout 0.35 g/cc. (loose), and from about 0.38 to about 0.45 g/cc.(packed), respectively. The blended mixture is slugged at 1/4 inchdiameter, the slug density being adjusted to give a granulated pill mixwith a packed A.B.D. in the range from about 0.40 to about 0.5 g/cc.Larger or smaller diameter slugs may be made, densities being slightlylower for the larger diameters. The slugs obtained are granulated usinga coarse screen so as to obtain a powder having an A.B.D. in the rangefrom about 0.35 to about 0.45 g/cc. (loose) and from about 0.45 to about0.55 g/cc. (packed).

The granulated powder obtained is tableted in any convenient size, 1/4diameter × 1/4 inch long being preferred. The tablets are then calcinedin a tunnel kiln at a temperature in the range from about 1000°C toabout 1200°C so that the calcined pills have a surface area in the rangefrom about 50 m² /gm. to about 150 m² /gm.

The calcined tablets are cooled and impregnated with a cobalt sulfatesolution to give a final cobalt content in the range from about 4 toabout 5 percent. The wet tablets, after being dried in a conventionalconvection oven at about 120°C until essentially dry (L.O.I. in therange from 3-5% at 600°C) have a specific gravity in the range fromabout 0.5 to about 0.7. Calcined crush strength of supported catalyst isin excess of 20 lbs. and a fixed bed reactor packed with tabletsprepared as described hereinabove, and operated in a conventionalmanner, withstood continuous use in desulfurizing stack gases withoutdegradation. The crush strength of the tablets is essentially the sameprior to and after use in the reactor. By "essentially the same" ismeant that, on a statistical basis, fresh and used catalyst differ incrush strength by about 10 percent or less. The reactor is operatedcontinuously for a prolonged period of time without loss of activity ofthe catalyst and with an inconsequentially slight increase in pressuredrop.

What is claimed is:
 1. A catalyst composition consisting essentially ofcobalt sulfate deposited in a finely divided crystalline form as theessential catalytic ingredient on a catalyst support.
 2. Adesulfurization catalyst for the single step conversion of sulfur oxidesto elemental sulfur in the presence of reducing gases containing carbonmonoxide as an essential reductant, said catalyst consisting essentiallyof cobalt sulfate in a finely divided crystalline form supported on acatalyst support, said desulfurization catalyst containing from about1/2 to about 10 parts by weight cobalt per hundred parts by weightsupported catalyst.
 3. The desulfurization catalyst of claim 2 whereinsaid catalyst support comprises porous gamma-alumina.
 4. Thedesulfurization catalyst of claim 3 wherein said catalyst supportincludes, in addition, clay.
 5. The desulfurization catalyst of claim 4wherein said clay is bentonite.
 6. The desulfurization catalyst or claim2 wherein said catalyst is tableted, pelleted, or spherodized.
 7. Thedesulfurization catalyst of claim 4 wherein the specific gravity of atablet or pellet is in the range from about 0.5 to about 0.7.
 8. Thedesulfurization catalyst of claim 7 wherein the tablet or pellet has asurface area in the range from about 40 to about 200 M² /gm.
 9. Thedesulfurization catalyst of claim 6 wherein the pellet has essentiallythe same crush strength before and after use in a desulfurizationreaction.
 10. The desulfurization catalyst of claim 5 wherein saidcatalyst support contains from about 5 to about 50 percent by weightbentonite.